When I plug my Gemma into a USB 2 hub and reset it, the red LED comes on for about 2 seconds and then turns off. It doesn't blink and it doesn't appear to get dim. When I try to upload code to it I get:

avrdude: Error: Could not find USBtiny device (0x1781/0xc9f)

Tools > Board = Adafruit Gemma 8MHzTools > Programmer = USBtinyISP

The hub is connect to my Mac's USB 3 port. I've tried a different USB 2 hub. I've tried a different USB cable.

I ordered another Gemma, same thing.

I ordered an Arduino Uno and loaded the "trinket loader" on it, then wired it to the Gemma (as described in "Introducing Trinket"), including attaching the reset pin. The sketch appears to work, but it doesn't change the Gemma's boot loader. The sketch outputs:

Type 'G' or hit BUTTON for next chipStarting Program Mode [OK]

Reading signature:930BSearching for image... Found "blankfull.hex" for attiny85

I have two Trinkets and when I plugged them into my hub, they also didn't blink. That's when I decided the problem must be in the hub or cables. There's just no way this many are bad out of the box. (I've been using 2', 3', and 6' cables to test.)

I have a Charger Doctor I bought from Adafruit and I put it on the USB hub. It shows 5.18V. Have I been blowing up my Trinkets and Gemmas with this powered USB hub?

I've confirmed that I'm using a data cable, though it turns out I did have some charge-only cables in the mix and didn't realize it. (I didn't even realize charge-only cables existed.)

But my devices still boot red, then flicker once, then off in about 3 seconds.

I'm going to order a new 5V Trinket for one last try. I can't guess at all what's wrong with these devices. Could I return them to you? I don't even want my money back, I just want to know what's gone wrong and how to avoid this in the future.

I got a new Trinket and it didn't work and then I found the real problem.

My powered hub, which works with my mouse, keyboard, phone, Arduino Uno, and Arduino Mega... does not work with the Gemma or Trinket. I tried a different hub and it worked... Not only with the new Trinket, but with all of the old Gemmas and Trinkets I had.

The reason I didn't catch this before, when I tried a different hub, was probably because I was using one of the charge-only cables when I swapped hubs.

I just can't imagine why this particular hub isn't working, but for the number of hours I spent on this I will never let it be my friend again.

FWIW, when the Gemma or Trinket is getting whatever it needs for a good bootload cycle, the red LED is full-on bright... significantly brighter than the green LED. When it wasn't working, it was about half the brightness of the green LED.

Actually, I loved the form factor of this hub. KB, mouse, and phone charging/data ports on the back, top port for flash drives or Arduino... in theory. It might be just this hub, which is a couple of years old.